This chapter contains sections titled: Rationale for narrow-band imaging application Historical background of narrow-band imaging The blue light physical principle Using the narrow-band imaging system at the endoscopy unit Difference between conventional chromoendoscopy and narrow-band imaging Narrow-band imaging for screening colonoscopy Narrow-band imaging for non-neoplastic and neoplastic lesions Meshed capillary vessels by narrow-band imaging Benefit of in vivo diagnosis of small colorectal polyps Nonmagnifying narrow-band imaging system Narrow-band imaging for noninvasive and invasive colorectal cancer Vessel diameter measured by immunohistochemistry Rationale for differences in size of meshed capillary vessels in colorectal polyps—the Toppan test The Sano–Emura narrow-band imaging classification of the capillary pattern Detection of dysplastic areas in ulcerative colitis Future perspective Acknowledgments References